Linux I2C驱动分析(三)----i2c_dev驱动和应用层分析【转】

本文转载自：http://blog.chinaunix.net/uid-21558711-id-3959287.html

分类： LINUX

原文地址：Linux I2C驱动分析(三)----i2c_dev驱动和应用层分析作者：apple_guet

1.1、设备驱动注册

分析这个驱动，还是从module_init()和module_exit()开始，程序如下：

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static int __init i2c_dev_init(void)

{

int res;

printk(KERN_INFO "i2c /dev entries driver\n");

res = register_chrdev(I2C_MAJOR, "i2c", &i2cdev_fops);

if (res)

goto out;

i2c_dev_class = class_create(THIS_MODULE, "i2c-dev");

if (IS_ERR(i2c_dev_class)) {

res = PTR_ERR(i2c_dev_class);

goto out_unreg_chrdev;

}

/* Keep track of adapters which will be added or removed later */

res = bus_register_notifier(&i2c_bus_type, &i2cdev_notifier);

if (res)

goto out_unreg_class;

/* Bind to already existing adapters right away */

i2c_for_each_dev(NULL, i2cdev_attach_adapter);

return 0;

out_unreg_class:

class_destroy(i2c_dev_class);

out_unreg_chrdev:

unregister_chrdev(I2C_MAJOR, "i2c");

out:

printk(KERN_ERR "%s: Driver Initialisation failed\n", __FILE__);

return res;

}

static void __exit i2c_dev_exit(void)

{

bus_unregister_notifier(&i2c_bus_type, &i2cdev_notifier);

i2c_for_each_dev(NULL, i2cdev_detach_adapter);

class_destroy(i2c_dev_class);

unregister_chrdev(I2C_MAJOR, "i2c");

}

module_init(i2c_dev_init);

module_exit(i2c_dev_exit);

首先注册了i2cdev_fops操作函数集，接着注册了一个名为”i2c-dev”的class，然后又注册了一个i2cdev_notifier，i2cdev_notifier如下：

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static struct notifier_block i2cdev_notifier = {

.notifier_call = i2cdev_notifier_call,

};

int i2cdev_notifier_call(struct notifier_block *nb, unsigned long action,

void *data)

{

struct device *dev = data;

switch (action) {

case BUS_NOTIFY_ADD_DEVICE:

return i2cdev_attach_adapter(dev, NULL);

case BUS_NOTIFY_DEL_DEVICE:

return i2cdev_detach_adapter(dev, NULL);

}

return 0;

}

紧接着看下i2cdev_attach_adapter函数：

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static int i2cdev_attach_adapter(struct device *dev, void *dummy)

{

struct i2c_adapter *adap;

struct i2c_dev *i2c_dev;

int res;

if (dev->type != &i2c_adapter_type)

return 0;

adap = to_i2c_adapter(dev);

i2c_dev = get_free_i2c_dev(adap);

if (IS_ERR(i2c_dev))

return PTR_ERR(i2c_dev);

/* register this i2c device with the driver core */

i2c_dev->dev = device_create(i2c_dev_class, &adap->dev,

MKDEV(I2C_MAJOR, adap->nr), NULL,

"i2c-%d", adap->nr);

if (IS_ERR(i2c_dev->dev)) {

res = PTR_ERR(i2c_dev->dev);

goto error;

}

res = device_create_file(i2c_dev->dev, &dev_attr_name);

if (res)

goto error_destroy;

pr_debug("i2c-dev: adapter [%s] registered as minor %d\n",

adap->name, adap->nr);

return 0;

error_destroy:

device_destroy(i2c_dev_class, MKDEV(I2C_MAJOR, adap->nr));

error:

return_i2c_dev(i2c_dev);

return res;

}

        这个函数也很简单，首先调用get_free_i2c_dev()分配并初始化了一个struct i2c_dev结构，使i2c_dev->adap指向操作的adapter.之后，该i2c_dev会被链入链表i2c_dev_list中。再分别以I2C_MAJOR,、adap->nr为主次设备号创建了一个device。如果此时系统配置了udev或者是hotplug,那么就在/dev下自动创建相关的设备节点了。
        i2cdev_detach_adapter函数完成相反的操作，在此省略。
        所有主设备号为I2C_MAJOR的设备节点的操作函数是i2cdev_fops，它的定义如下所示：

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static const struct file_operations i2cdev_fops = {

.owner = THIS_MODULE,

.llseek = no_llseek,

.read = i2cdev_read,

.write = i2cdev_write,

.unlocked_ioctl = i2cdev_ioctl,

.open = i2cdev_open,

.release = i2cdev_release,

};

接下来一一分析i2cdev_fops结构体的成员。

1.2、设备打开函数--i2cdev_open

点击(此处)折叠或打开

static int i2cdev_open(struct inode *inode, struct file *file)

{

unsigned int minor = iminor(inode);

struct i2c_client *client;

struct i2c_adapter *adap;

struct i2c_dev *i2c_dev;

i2c_dev = i2c_dev_get_by_minor(minor); //以次设备号从i2c_dev_list链表中取得i2c_dev

if (!i2c_dev)

return -ENODEV;

adap = i2c_get_adapter(i2c_dev->adap->nr); //以apapter的总线号从i2c_adapter_idr中找到adapter

if (!adap)

return -ENODEV;

/* This creates an anonymous i2c_client, which may later be

* pointed to some address using I2C_SLAVE or I2C_SLAVE_FORCE.

* This client is ** NEVER REGISTERED ** with the driver model

* or I2C core It just holds private copies of addressing

* information and maybe a PEC flag.

client = kzalloc(sizeof(*client), GFP_KERNEL); //分配并初始化一个i2c_client结构

if (!client) {

i2c_put_adapter(adap);

return -ENOMEM;

}

snprintf(client->name, I2C_NAME_SIZE, "i2c-dev %d", adap->nr);

client->adapter = adap; //clinet->adapter指向操作的adapter

file->private_data = client; //关联到file

return 0;

}

注意这里分配并初始化了一个struct i2c_client结构，但是没有注册这个clinet。此外，这个函数中还有一个比较奇怪的操作，不是在前面已经将i2c_dev->adap 指向要操作的adapter么？为什么还要以adapter->nr为关键字从i2c_adapter_idr去找这个操作的adapter呢？因为调用i2c_get_adapter()从总线号nr找到操作的adapter的时候，还会增加module的引用计数，这样可以防止模块意外被释放掉，那 i2c_dev->adap->nr操作，如果i2c_dev->adap被释放掉的话，不是会引起系统崩溃么？这里因为在 i2cdev_attach_adapter()间接的增加了一次adapter的一次引用计数.如下:

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static int i2cdev_attach_adapter(struct i2c_adapter *adap)

{

．．．．．．

i2c_dev->dev = device_create(i2c_dev_class, &adap->dev,

MKDEV(I2C_MAJOR, adap->nr),

"i2c-%d", adap->nr);

．．．．．．

}

i2c_dev内嵌的device是以adap->dev为父结点，在device_create()中会增次adap->dev的一次引用计数。

1.3、read操作

Read操作对应的操作函数如下示:

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static ssize_t i2cdev_read (struct file *file, char __user *buf, size_t count,

loff_t *offset)

{

char *tmp;

int ret;

struct i2c_client *client = (struct i2c_client *)file->private_data;

if (count > 8192)

count = 8192;

tmp = kmalloc(count,GFP_KERNEL);

if (tmp==NULL)

return -ENOMEM;

pr_debug("i2c-dev: i2c-%d reading %zd bytes./n",

iminor(file->f_path.dentry->d_inode), count);

ret = i2c_master_recv(client,tmp,count);

if (ret >= 0)

ret = copy_to_user(buf,tmp,count)?-EFAULT:ret;

kfree(tmp);

return ret;

}

首先从file结构中取得struct i2c_clinet，然后在kernel分配相同长度的缓存区，随之调用i2c_master_recv()从设备中读取数据.再将读取出来的数据copy到用户空间中。I2c_master_recv()在《Linux I2C驱动分析(二)----I2C板级设备扫描和数据传输》已经讲述。

1.4、write操作

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static ssize_t i2cdev_write(struct file *file, const char __user *buf,

size_t count, loff_t *offset)

{

int ret;

char *tmp;

struct i2c_client *client = file->private_data;

if (count > 8192)

count = 8192;

tmp = memdup_user(buf, count);

if (IS_ERR(tmp))

return PTR_ERR(tmp);

pr_debug("i2c-dev: i2c-%d writing %zu bytes.\n",

iminor(file->f_path.dentry->d_inode), count);

ret = i2c_master_send(client, tmp, count);

kfree(tmp);

return ret;

}

该操作比较简单，就是将用户空间的数据通过使用函数i2c_master_send发送到i2c 设备。i2c_master_send函数在《Linux I2C驱动分析(二)----I2C板级设备扫描和数据传输》已经讲述。

memdup_user函数完成分配存储区，把应用层的数据复制到刚分配的存储区中，具体程序如下：

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void *memdup_user(const void __user *src, size_t len)

{

void *p;

* Always use GFP_KERNEL, since copy_from_user() can sleep and

* cause pagefault, which makes it pointless to use GFP_NOFS

* or GFP_ATOMIC.

p = kmalloc_track_caller(len, GFP_KERNEL);

if (!p)

return ERR_PTR(-ENOMEM);

if (copy_from_user(p, src, len)) {

kfree(p);

return ERR_PTR(-EFAULT);

}

return p;

}

1.5、 ioctl函数

有人可能看出了一个问题，clinet->addr是从哪来的呢？对，在read之前应该还要有一步操作来设置 clinet->addr的值。这个过程是ioctl的操作，ioctl可以设置PEC标志，重试次数，超时时间和发送接收数据等。具体程序如下：

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static long i2cdev_ioctl(struct file *file, unsigned int cmd, unsigned long arg)

{

struct i2c_client *client = file->private_data;

unsigned long funcs;

dev_dbg(&client->adapter->dev, "ioctl, cmd=0x%02x, arg=0x%02lx\n",

cmd, arg);

switch (cmd) {

case I2C_SLAVE:

case I2C_SLAVE_FORCE:

/* NOTE: devices set up to work with "new style" drivers

* can't use I2C_SLAVE, even when the device node is not

* bound to a driver. Only I2C_SLAVE_FORCE will work.

* Setting the PEC flag here won't affect kernel drivers,

* which will be using the i2c_client node registered with

* the driver model core. Likewise, when that client has

* the PEC flag already set, the i2c-dev driver won't see

* (or use) this setting.

if ((arg > 0x3ff) ||

(((client->flags & I2C_M_TEN) == 0) && arg > 0x7f))

return -EINVAL;

if (cmd == I2C_SLAVE && i2cdev_check_addr(client->adapter, arg))

return -EBUSY;

/* REVISIT: address could become busy later */

client->addr = arg; //设置addr

return 0;

case I2C_TENBIT:

//设置10 bit地址模式

if (arg)

client->flags |= I2C_M_TEN;

else

client->flags &= ~I2C_M_TEN;

return 0;

case I2C_PEC:

//设置传输后增加PEC标志

if (arg)

client->flags |= I2C_CLIENT_PEC;

else

client->flags &= ~I2C_CLIENT_PEC;

return 0;

case I2C_FUNCS:

//获取函数支持

funcs = i2c_get_functionality(client->adapter);

return put_user(funcs, (unsigned long __user *)arg);

case I2C_RDWR:

//读取和接收数据，后面讲述

return i2cdev_ioctl_rdrw(client, arg);

case I2C_SMBUS:

//smbus协议数据传输，后面讲述

return i2cdev_ioctl_smbus(client, arg);

case I2C_RETRIES:

//设置重试次数

client->adapter->retries = arg;

break;

case I2C_TIMEOUT:

/* For historical reasons, user-space sets the timeout

* value in units of 10 ms.

//设置超时时间

client->adapter->timeout = msecs_to_jiffies(arg * 10);

break;

default:

/* NOTE: returning a fault code here could cause trouble

* in buggy userspace code. Some old kernel bugs returned

* zero in this case, and userspace code might accidentally

* have depended on that bug.

return -ENOTTY;

}

return 0;

}

读取和接收数据函数i2cdev_ioctl_rdrw(client, arg);如下：

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static noinline int i2cdev_ioctl_rdrw(struct i2c_client *client,

unsigned long arg)

{

struct i2c_rdwr_ioctl_data rdwr_arg; //包括i2c_msg和它的个数

struct i2c_msg *rdwr_pa;

u8 __user **data_ptrs;

int i, res;

if (copy_from_user(&rdwr_arg,

(struct i2c_rdwr_ioctl_data __user *)arg,

sizeof(rdwr_arg)))

return -EFAULT;

/* Put an arbitrary limit on the number of messages that can

* be sent at once */

if (rdwr_arg.nmsgs > I2C_RDRW_IOCTL_MAX_MSGS)

return -EINVAL;

rdwr_pa = kmalloc(rdwr_arg.nmsgs * sizeof(struct i2c_msg), GFP_KERNEL); //创建存储i2c_msg的内存

if (!rdwr_pa)

return -ENOMEM;

if (copy_from_user(rdwr_pa, rdwr_arg.msgs,

rdwr_arg.nmsgs * sizeof(struct i2c_msg))) {

kfree(rdwr_pa);

return -EFAULT;

}

data_ptrs = kmalloc(rdwr_arg.nmsgs * sizeof(u8 __user *), GFP_KERNEL);

if (data_ptrs == NULL) {

kfree(rdwr_pa);

return -ENOMEM;

}

res = 0;

for (i = 0; i < rdwr_arg.nmsgs; i++) {

/* Limit the size of the message to a sane amount;

* and don't let length change either. */

if ((rdwr_pa[i].len > 8192) ||

(rdwr_pa[i].flags & I2C_M_RECV_LEN)) {

res = -EINVAL;

break;

}

data_ptrs[i] = (u8 __user *)rdwr_pa[i].buf;

rdwr_pa[i].buf = memdup_user(data_ptrs[i], rdwr_pa[i].len);

if (IS_ERR(rdwr_pa[i].buf)) {

res = PTR_ERR(rdwr_pa[i].buf);

break;

}

if (res < 0) {

int j;

for (j = 0; j < i; ++j)

kfree(rdwr_pa[j].buf);

kfree(data_ptrs);

kfree(rdwr_pa);

return res;

}

res = i2c_transfer(client->adapter, rdwr_pa, rdwr_arg.nmsgs); //传输数据

while (i-- > 0) {

if (res >= 0 && (rdwr_pa[i].flags & I2C_M_RD)) {

if (copy_to_user(data_ptrs[i], rdwr_pa[i].buf,

rdwr_pa[i].len)) //将接收到的数据发送到应用层

res = -EFAULT;

}

kfree(rdwr_pa[i].buf);

}

kfree(data_ptrs);

kfree(rdwr_pa);

return res;

}

smbus协议数据传输函数i2cdev_ioctl_smbus(client, arg);如下：

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static noinline int i2cdev_ioctl_smbus(struct i2c_client *client,

unsigned long arg)

{

struct i2c_smbus_ioctl_data data_arg;

union i2c_smbus_data temp;

int datasize, res;

//从应用层复制数据

if (copy_from_user(&data_arg,

(struct i2c_smbus_ioctl_data __user *) arg,

sizeof(struct i2c_smbus_ioctl_data)))

return -EFAULT;

if ((data_arg.size != I2C_SMBUS_BYTE) &&

(data_arg.size != I2C_SMBUS_QUICK) &&

(data_arg.size != I2C_SMBUS_BYTE_DATA) &&

(data_arg.size != I2C_SMBUS_WORD_DATA) &&

(data_arg.size != I2C_SMBUS_PROC_CALL) &&

(data_arg.size != I2C_SMBUS_BLOCK_DATA) &&

(data_arg.size != I2C_SMBUS_I2C_BLOCK_BROKEN) &&

(data_arg.size != I2C_SMBUS_I2C_BLOCK_DATA) &&

(data_arg.size != I2C_SMBUS_BLOCK_PROC_CALL)) {

dev_dbg(&client->adapter->dev,

"size out of range (%x) in ioctl I2C_SMBUS.\n",

data_arg.size);

return -EINVAL; //不符合协议，直接退出

}

/* Note that I2C_SMBUS_READ and I2C_SMBUS_WRITE are 0 and 1,

so the check is valid if size==I2C_SMBUS_QUICK too. */

if ((data_arg.read_write != I2C_SMBUS_READ) &&

(data_arg.read_write != I2C_SMBUS_WRITE)) {

dev_dbg(&client->adapter->dev,

"read_write out of range (%x) in ioctl I2C_SMBUS.\n",

data_arg.read_write);

return -EINVAL; //既不是读，也不是写

}

/* Note that command values are always */

if ((data_arg.size == I2C_SMBUS_QUICK) ||

((data_arg.size == I2C_SMBUS_BYTE) &&

(data_arg.read_write == I2C_SMBUS_WRITE)))

/* These are special: we do not use data */

return i2c_smbus_xfer(client->adapter, client->addr,

client->flags, data_arg.read_write,

data_arg.command, data_arg.size, NULL); //不需要读

if (data_arg.data == NULL) {

dev_dbg(&client->adapter->dev,

"data is NULL pointer in ioctl I2C_SMBUS.\n");

return -EINVAL;

}

//判断数据大小

if ((data_arg.size == I2C_SMBUS_BYTE_DATA) ||

(data_arg.size == I2C_SMBUS_BYTE))

datasize = sizeof(data_arg.data->byte);

else if ((data_arg.size == I2C_SMBUS_WORD_DATA) ||

(data_arg.size == I2C_SMBUS_PROC_CALL))

datasize = sizeof(data_arg.data->word);

else /* size == smbus block, i2c block, or block proc. call */

datasize = sizeof(data_arg.data->block);

if ((data_arg.size == I2C_SMBUS_PROC_CALL) ||

(data_arg.size == I2C_SMBUS_BLOCK_PROC_CALL) ||

(data_arg.size == I2C_SMBUS_I2C_BLOCK_DATA) ||

(data_arg.read_write == I2C_SMBUS_WRITE)) {

if (copy_from_user(&temp, data_arg.data, datasize))

return -EFAULT;

}

if (data_arg.size == I2C_SMBUS_I2C_BLOCK_BROKEN) {

/* Convert old I2C block commands to the new

convention. This preserves binary compatibility. */

data_arg.size = I2C_SMBUS_I2C_BLOCK_DATA;

if (data_arg.read_write == I2C_SMBUS_READ)

temp.block[0] = I2C_SMBUS_BLOCK_MAX;

}

//smbus数据传输，2中已经讲述

res = i2c_smbus_xfer(client->adapter, client->addr, client->flags,

data_arg.read_write, data_arg.command, data_arg.size, &temp);

if (!res && ((data_arg.size == I2C_SMBUS_PROC_CALL) ||

(data_arg.size == I2C_SMBUS_BLOCK_PROC_CALL) ||

(data_arg.read_write == I2C_SMBUS_READ))) {

if (copy_to_user(data_arg.data, &temp, datasize))

return -EFAULT;

}

return res;

}

二、用户空间使用i2c_dev

对于注册的i2c适配器，用户空间可以使用它们。上面的驱动对每个适配器生成一个主设备号为89的设备节点，实现了文件操作接口，用户空间可以通过i2c设备节点访问i2c适配器。适配器的编号从0开始，和适配器的设备节点的次设备号相同。i2c适配器的设备节点是/dev/i2c-x，其中x是数字，代表适配器的编号。由于适配器编号是动态分配的（和注册次序有关），所以想了解哪一个适配器对应什么编号，可以查看/sys/class/i2c-dev/目录下的文件内容。

2.1 前期准备

为了在用户空间的程序当中操作i2c适配器，必须在程序中包含以下两句：

点击(此处)折叠或打开

#include<linux/i2c-dev.h>

#include<linux/i2c.h>

这两个头文件中定义了之后需要用到的结构体和宏。然后就可以打开设备节点了。但是打开哪一个呢？因为适配器的编号并不固定。为此我们在终端中运行以下命令：

[root@hdw /]# cat /sys/class/i2c-dev/i2c-0/name

BLX GSC3280 I2C adapter

如果我们想打开第二个适配器，刚好它的编号是1，对应的设备节点是/dev/i2c-1。那么可以用下面的方法打开它：

点击(此处)折叠或打开

int fd;

if ((fd = open(＂/dev/i2c-1＂,O_RDWR))< 0)

{

/* 错误处理 */

exit(1);

}

打开适配器对应的设备节点，i2c-dev为打开的线程建立一个i2c_client，但是这个i2c_client并不加到i2c_adapter的client链表当中。当用户关闭设备节点时，它自动被释放。

2.2 IOCTL控制

查看include/linux/i2c-dev.h文件，可以看到i2c-dev支持的IOCTL命令。如下：

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#define I2C_RETRIES 0x0701 /* 设置收不到ACK时的重试次数 */

#define I2C_TIMEOUT 0x0702 /* 设置超时时限的jiffies */

#define I2C_SLAVE 0x0703 /* 设置从机地址 */

#define I2C_SLAVE_FORCE 0x0706 /* 强制设置从机地址 */

#define I2C_TENBIT 0x0704 /* 选择地址位长:=0 for 7bit , != 0 for 10 bit */

#define I2C_FUNCS 0x0705 /* 获取适配器支持的功能 */

#define I2C_RDWR 0x0707 /* Combined R/W transfer (one STOP only) */

#define I2C_PEC 0x0708 /* != 0 to use PEC with SMBus */

#define I2C_SMBUS 0x0720 /* SMBus transfer */

下面进行一一解释。

1．设置重试次数

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ioctl(fd, I2C_RETRIES, m); //这句话设置适配器收不到ACK时重试的次数为m。默认的重试次数为1。

2．设置超时

点击(此处)折叠或打开

ioctl(fd, I2C_TIMEOUT, m); //设置SMBus的超时时间为m，单位为jiffies。

3．设置从机地址

点击(此处)折叠或打开

ioctl(fd, I2C_SLAVE,addr);

ioctl(fd, I2C_SLAVE_FORCE, addr);

在调用read()和write()函数之前必须设置从机地址。这两行都可以设置从机的地址，区别是第二行无论内核中是否已有驱动在使用这个地址都会成功，第一行则只在该地址空闲的情况下成功。由于i2c-dev创建的i2c_client不加入i2c_adapter的client列表，所以不能防止其它线程使用同一地址，也不能防止驱动模块占用同一地址。

4．设置地址模式

点击(此处)折叠或打开

ioctl(file, I2C_TENBIT, select); //如果select不等于0选择10比特地址模式，如果等于0选择7比特模式，默认7比特。只有适配器支持I2C_FUNC_10BIT_ADDR，这个请求才是有效的。

5．获取适配器功能

点击(此处)折叠或打开

ioctl(file, I2C_FUNCS, （unsignedlong *）funcs); //获取的适配器功能保存在funcs中。各比特的含义如:

/* include/linux/i2c.h */

#define I2C_FUNC_I2C 0x00000001

#define I2C_FUNC_10BIT_ADDR 0x00000002

#define I2C_FUNC_PROTOCOL_MANGLING 0x00000004 /* I2C_M_{REV_DIR_ADDR,NOSTART,..} */

#define I2C_FUNC_SMBUS_PEC 0x00000008

#define I2C_FUNC_SMBUS_BLOCK_PROC_CALL 0x00008000 /* SMBus 2.0 */

#define I2C_FUNC_SMBUS_QUICK 0x00010000

#define I2C_FUNC_SMBUS_READ_BYTE 0x00020000

#define I2C_FUNC_SMBUS_WRITE_BYTE 0x00040000

#define I2C_FUNC_SMBUS_READ_BYTE_DATA 0x00080000

#define I2C_FUNC_SMBUS_WRITE_BYTE_DATA 0x00100000

#define I2C_FUNC_SMBUS_READ_WORD_DATA 0x00200000

#define I2C_FUNC_SMBUS_WRITE_WORD_DATA 0x00400000

#define I2C_FUNC_SMBUS_PROC_CALL 0x00800000

#define I2C_FUNC_SMBUS_READ_BLOCK_DATA 0x01000000

#define I2C_FUNC_SMBUS_WRITE_BLOCK_DATA 0x02000000

#define I2C_FUNC_SMBUS_READ_I2C_BLOCK 0x04000000 /* I2C-like block xfer */

#define I2C_FUNC_SMBUS_WRITE_I2C_BLOCK 0x08000000 /* w/ 1-byte reg. addr. */

#define I2C_FUNC_SMBUS_READ_I2C_BLOCK_2 0x10000000 /* I2C-like block xfer */

#define I2C_FUNC_SMBUS_WRITE_I2C_BLOCK_2 0x20000000 /* w/ 2-byte reg. addr. */

6． I2C层通信

点击(此处)折叠或打开

ioctl(file, I2C_RDWR, (structi2c_rdwr_ioctl_data *)msgset);

这一行代码可以使用I2C协议和设备进行通信。它进行连续的读写，中间没有间歇。只有当适配器支持I2C_FUNC_I2C此命令才有效。参数是一个指针，指向一个结构体，它的定义如：

点击(此处)折叠或打开

struct i2c_rdwr_ioctl_data {

struct i2c_msg __user *msgs; /* 指向i2c_msgs数组 */

__u32nmsgs; /* 消息的个数 */

};

msgs[] 数组成员包含了指向各自缓冲区的指针。这个函数会根据是否在消息中的flags置位I2C_M_RD来对缓冲区进行读写。从机的地址以及是否使用10比特地址模式记录在每个消息中，忽略之前ioctl设置的结果。

7．设置SMBus PEC

点击(此处)折叠或打开

ioctl(file, I2C_PEC, (long )select);

如果select不等于0选择SMBus PEC (packet error checking)，等于零则关闭这个功能，默认是关闭的。

这个命令只对SMBus传输有效。这个请求只在适配器支持I2C_FUNC_SMBUS_PEC时有效；如果不支持这个命令也是安全的，它不做任何工作。

8．SMBus通信

点击(此处)折叠或打开

ioctl(file, I2C_SMBUS, (i2c_smbus_ioctl_data*)msgset);

这个函数和I2C_RDWR类似，参数的指针指向i2c_smbus_ioctl_data类型的变量，它的定义如：

点击(此处)折叠或打开

struct i2c_smbus_ioctl_data {

__u8read_write;

__u8command;

__u32size;

unioni2c_smbus_data __user *data;

};

2.3 i2c_dev使用例程

要想在用户空间使用i2c适配器，首先要选择某个适配器的设备节点打开，然后才能进行通信。

2.3.1 read()/write()

通信的方式有两种，一种是使用操作普通文件的接口read()和write()。这两个函数间接调用了i2c_master_recv和 i2c_master_send。但是在使用之前需要使用I2C_SLAVE设置从机地址，设置可能失败，需要检查返回值。这种通信过程进行I2C层的通信，一次只能进行一个方向的传输。

下面的程序是ARM与E2PROM芯片通信的例子，使用read()/write()与i2c设备通信：

点击(此处)折叠或打开

#include <stdio.h>

#include <sys/ioctl.h>

#include <fcntl.h>

#include <linux/i2c-dev.h>

#include <linux/i2c.h>

#define CHIP "/dev/i2c-0"
#define CHIP_ADDR 0x50

int main()

{

printf("this is i2c test/n");

int fd =open(CHIP, O_RDWR);

if (fd< 0) {

printf("open"CHIP"failed/n");

gotoexit;

}

if (ioctl(fd, I2C_SLAVE_FORCE, CHIP_ADDR) < 0) {

/* 设置芯片地址 */

printf("oictl:setslave address failed/n");

goto close;

}

struct i2c_msg msg;

unsigned char rddata;

unsigned char rdaddr[2] = {0, 0}; /* 将要读取的数据在芯片中的偏移量 */

unsigned char wrbuf[3] = {0, 0, 0x3c}; /* 要写的数据，头两字节为偏移量 */

printf("inputa char you want to write to E2PROM/n");

wrbuf[2]= getchar();

printf("writereturn:%d, write data:%x/n", write(fd, wrbuf, 3), wrbuf[2]);

sleep(1);

printf("writeaddress return: %d/n",write(fd, rdaddr, 2)); /* 读取之前首先设置读取的偏移量 */

printf("readdata return:%d/n", read(fd, &rddata, 1));

printf("rddata:%c/n", rddata);

close:

close(fd);

exit:

return0;

}

1.3.2 I2C_RDWR

还可以使用I2C_RDWR实现同样的功能，使用I2C_RDWR与I2C设备通信

点击(此处)折叠或打开

#include <stdio.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <linux/i2c-dev.h>
#include <linux/i2c.h>

#define CHIP "/dev/i2c-0"
#define CHIP_ADDR 0x50
int main()
{
printf("hello,this is i2c tester/n");
int fd =open(CHIP, O_RDWR);
if (fd< 0) {
printf("open"CHIP"failed/n");
gotoexit;
}
struct i2c_msg msg;
unsigned char rddata;
unsigned char rdaddr[2] = {0, 0};
unsigned char wrbuf[3] = {0, 0, 0x3c};
printf("inputa char you want to write to E2PROM/n");
wrbuf[2]= getchar();
struct i2c_rdwr_ioctl_data ioctl_data;
struct i2c_msg msgs[2];
msgs[0].addr= CHIP_ADDR;
msgs[0].len= 3;
msgs[0].buf= wrbuf;
ioctl_data.nmsgs= 1;
ioctl_data.msgs= &msgs[0];
printf("ioctlwrite,return :%d/n", ioctl(fd, I2C_RDWR, &ioctl_data));
sleep(1);
msgs[0].addr= CHIP_ADDR;
msgs[0].len= 2;
msgs[0].buf= rdaddr;
msgs[1].addr= CHIP_ADDR;
msgs[1].flags|= I2C_M_RD;
msgs[1].len= 1;
msgs[1].buf= &rddata;
ioctl_data.nmsgs= 1;
ioctl_data.msgs= msgs;
printf("ioctlwrite address, return :%d/n", ioctl(fd, I2C_RDWR, &ioctl_data));
ioctl_data.msgs= &msgs[1];
printf("ioctlread, return :%d/n", ioctl(fd, I2C_RDWR, &ioctl_data));
printf("rddata:%c/n", rddata);
close:
close(fd);
exit:
return0;
}

1.1、设备驱动注册

1.2、设备打开函数--i2cdev_open

1.3、read操作

1.4、write操作

1.5、 ioctl函数

二、 用户空间使用i2c_dev

2.1 前期准备

2.2 IOCTL控制

2.3 i2c_dev使用例程

2.3.1 read()/write()

1.3.2 I2C_RDWR

二、用户空间使用i2c_dev